Image encoder and image decoder, image encoding method and image decoding method, image encoding program and image decoding program, and computer readable recording medium recorded with image encoding program and computer readable recording medium recorded with image decoding program

Abstract

An image encoder including: a predicted-image generating unit that generates a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating methods; a prediction-mode judging unit that evaluates prediction efficiency of a predicted image outputted from the predicted-image generating unit to judge a predetermined prediction mode; and an encoding unit that subjects an output of the prediction-mode judging unit to variable-length encoding. The prediction-mode judging unit judges, on the basis of a predetermined control signal, which one of a common prediction mode and a separate prediction mode is used for respective color components forming the input image signal, and multiplexes information on the control signal on a bit stream, multiplexes, when the common prediction mode is used, common prediction mode information on the bit stream, and multiplexes, when the common prediction mode is not used, prediction mode information for each of the color components on the bit stream.

1 . An image encoder that generates a bit stream, based on an input of a color image which is formed of a plurality of color components, by compression-encoding the color image in units of regions obtained by dividing the color image into predetermined regions, the image encoder comprising:
 a multiplexing unit that multiplexes common encoding/independent encoding identification information indicating whether the regions serving as the units of encoding are collectively encoded by a common prediction method for all the color components forming a signal, or the regions serving as the units of encoding are respectively encoded by a separate prediction method for respective color components; and   an encoding unit that uses an inter-prediction mode, a motion vector, and a reference image number which are commonly used for all the color components, in a case where the common encoding/independent encoding identification information indicates that the regions serving as the units of encoding are collectively encoded by a common prediction method for all the color components forming a signal, uses an inter-prediction mode, a motion vector, and a reference image number separately for respective color components, in a case where the common encoding/independent encoding identification information indicates the regions serving as the units of encoding are respectively encoded by a separate prediction method for respective color components, and compresses and encodes a prediction error signal obtained on the basis of the interprediction mode, the motion vector, and the reference image number.   
   
   
       2 . An image decoder, comprising:
 a prediction-mode decoding unit that decodes prediction modes separately encoded for respective color components forming the input image signal;   a predicted-image generating unit that generates a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating method; and   a decoding unit that generates a predicted image with the predicted-image generating unit on the basis of prediction modes of the respective color components set by the prediction-mode decoding unit to perform decoding to image data, wherein   the prediction-mode decoding unit refers to, in decoding a prediction mode allocated to a certain prediction unit, a lookup table obtained by tabulating combinations of states of a plurality of pieces of prediction mode information near the image region on an identical color component and predicted values for prediction modes of an encoding object to uniquely set a predicted value of prediction mode information from the states of the plurality of pieces of prediction mode Information near the image region and perform encoding.   
   
   
       3 . The Image encoder according to  claim 2 , wherein the prediction-mode decoding unit dynamically updates values of predicted values of prediction mode information in the lookup table on the basis of the states of the plurality of pieces of prediction mode information near the image region on the identical color component and the values of the decoded prediction modes. 
   
   
       4 . An image decoder, comprising:
 a prediction-mode decoding unit that decodes prediction modes separately encoded for respective color components forming the input image signal;   a predicted-image generating unit that generates a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating method; and   a decoding unit that generates a predicted image with the predicted-image generating unit on the basis of prediction modes of the respective color components set by the prediction-mode decoding unit to perform decoding to image data, wherein   the prediction-mode decoding unit performs, in decoding a prediction mode allocated to a certain prediction unit, arithmetic decoding while dynamically changing an occurrence probability according to a context set according to states of a plurality of pieces of prediction mode information near the image region on an identical color space in decoding a value of a prediction mode of a decoding object represented as a binary sequence for each bin of the binary sequence.   
   
   
       5 . The image decoder according to  claim 4 , wherein the prediction-mode decoding unit uses, as the context set according to the states of the plurality of pieces of prediction information near the image region on the identical color component, a state indicating into which of prediction in an image surface vertical direction and prediction in an image surface horizontal direction a prediction mode is classified. 
   
   
       6 . The image decoder according to  claim 4 , wherein the prediction-mode decoding unit uses, as the context set according to the states of the plurality of pieces of prediction information near the image region on the identical color component, a state indicating which of DC prediction and prediction other than the DC prediction a prediction mode is. 
   
   
       7 . An image decoding method for causing a computer to execute the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and referring to, in decoding a prediction mode allocated to a certain prediction unit, a lookup table obtained by tabulating combinations of states of a plurality of pieces of prediction mode information near the image region on an identical color component and predicted values for prediction modes of an encoding object to uniquely set a predicted value of prediction mode information from the states of the plurality of pieces of prediction mode information near the image region and perform decoding;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating methods; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of a prediction mode.   
   
   
       8 . An image decoding program for causing a computer to execute the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and referring to, in decoding a prediction mode allocated to a certain prediction unit, a lookup table obtained by tabulating combinations of states of a plurality of pieces of prediction mode information near the image region on an identical color component and predicted values for prediction modes of a decoding object to uniquely set a predicted value of prediction mode information from the states of the plurality of pieces of prediction mode information near the image region and perform decoding;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating methods; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of the prediction mode.   
   
   
       9 . A computer-readable recording medium recorded with an image decoding program for causing a computer to execute the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and referring to, in decoding a prediction mode allocated to a certain prediction unit, a lookup table obtained by tabulating combinations of states of a plurality of pieces of prediction mode information near the image region on an identical color component and predicted values for prediction modes of a decoding object to uniquely set a predicted value of prediction mode information from the states of the plurality of pieces of prediction mode information near the image region and perform decoding;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating methods; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of the prediction mode.   
   
   
       10 . An image decoding method, comprising the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and performing, in decoding a prediction mode allocated to a certain prediction unit, arithmetic decoding while dynamically changing an occurrence probability according to a context set according to states of a plurality of pieces of prediction mode information near the image region on an identical color space in decoding a value of a prediction mode of a decoding object represented as a binary sequence for each bin of the binary sequence;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating method; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of the prediction mode to perform decoding to image data.   
   
   
       11 . An image decoding program for causing a computer to execute the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and performing, in decoding a prediction mode allocated to a certain prediction unit, arithmetic decoding while dynamically changing an occurrence probability according to a context set according to states of a plurality of pieces of prediction mode information near the image region on an identical color space in decoding a value of a prediction mode of a decoding object represented as a binary sequence for each bin of the binary sequence;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating method; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of the prediction mode to perform decoding to image data.   
   
   
       12 . A computer-readable recording medium recorded with an image decoding program for causing a computer to execute the steps of:
 decoding prediction modes separately encoded for respective color components forming an input image signal and performing, in decoding a prediction mode allocated to a certain prediction unit, arithmetic decoding while dynamically changing an occurrence probability according to a context set according to states of a plurality of pieces of prediction mode information near the image region on an identical color space in decoding a value of a prediction mode of a decoding object represented as a binary sequence for each bin of the binary sequence;   generating a predicted image in accordance with a plurality of prediction modes indicating predicted-image generating method; and   generating a predicted image according to the step of generating a predicted image on the basis of prediction modes of the respective color components set in the step of performing decoding of the prediction mode to perform decoding to image data.